Re: announce: my very first disassembler now available (GPL)

On Aug 20, 5:43 pm, "H. Peter Anvin" <h...@xxxxxxxxx> wrote:
Alexei A. Frounze wrote:

Plain 90h, which would normally be XCHG EAX,EAX (and therefore
zero-extend EAX into RAX) is actually NOP.

I might have misspoken, but the appropriate REX followed by 0x90 isn't
a NOP, it's XCHG rAX, r8.

90 = nop = nop [would have been xchg eax,eax]
40 90 = rex nop = nop [would have been xchg eax,eax]

Yep.

41 90 = rex.b nop = xchg eax,r8d

Yep.

48 90 = rex.w nop = xchg rax,rax

Should be a NOP effectively.

49 90 = rex.wb nop = xchg rax,r8

Same here.

So, did you do the last two under a debugger? If you did, on what CPU
brand? Intel, AMD or both?

Alex
.

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